<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>0</h1>
<h2>0</h2>
<script>
    //开启定时器  每个一秒调用一次f方法
    setInterval(f,1000);
    let count = 0;
    function f(){
        count++;
        let h = document.querySelector("h1");
        h.innerText=count;
    }

    //匿名方法开启定时器
    let x=0;
    let timer = setInterval(function (){
        x++;
        let h =document.querySelector("h2")
        h.innerText=x;
        if(x>50){
            //停止定时器
            clearInterval(timer)
        }
    },100)

    //只执行一次的定时器
    setTimeout(function (){
        x=50;
    },3000)
</script>
</body>
</html>